Method for disseminating a message

ABSTRACT

In the present method for broadcasting a message in an incomplete radio communication network ( 2 ) having a fluctuating number of subscribers ( 4-12 ) for forwarding the message, with each subscriber having a transmitting and receiving device for messages and a positioning system for determining his global position, subscribers ( 6-12 ) determine their own position, and the distance d from the sender of the message, who is also a subscriber ( 6-12 ), after receiving the message, and transmit the message, with their own position, to further subscribers ( 6-12 ) after a predetermined waiting period t, which decreases monotonically as the distance d increases. This measure ensures a rapid transmission of the message that does not burden the radio communication network ( 2 ).

The invention relates to a method for broadcasting a message in anincomplete partial network of a radio communication network.

Methods for broadcasting messages are used, for example, in the field ofmobile, wireless communication, particularly in ad hoc networks. Inthese networks, the subscribers converge spontaneously and briefly. Thearrangement of the mobile subscribers of the network is arbitrary, andcan change with respect to space and time. An ad hoc network is normallya mobile, incomplete radio communication network with a decentralizedcontrol.

A radio network is only considered complete if a direct radio connectionexists between each subscriber pair. Each subscriber is equipped with aradio device, so he can communicate with other subscribers within range.There is no central entity that controls or checks the radio networkstructured in this manner. Furthermore, the subscribers have localclocks that are equipped with a synchronized time resolution.

Ad hoc networks occur, for example, when mobile computers (laptops,palmtops, etc.) converge at a conference. A plurality of robotscommunicating with one another and moving in terrain that is difficultto access, such as in deep space, under water or on a battlefield, etc.,can also constitute an ad hoc network.

Moreover, there are already miniature devices that are equipped withcommunication capabilities and are worn on a person. An example is adevice named “Lovegety” by the Erfolg Co. of Japan, which is describedin, among other things, the “Personals” section of the Tagesspiegel[Daily Mirror] of Jun. 3, 1998, and is intended to help people find asuitable partner. In the future, such devices will be able to form adhoc networks for performing more complex tasks.

Finally, this application encompasses radio-based, directvehicle-to-vehicle communication.

In the methods known from the state of the technology for broadcastingmessages, the identified communication partners must know the addressesto which the messages are to be sent. If this prerequisite is not met,the known methods cannot be employed, because the necessary informationis exceedingly difficult to obtain. Moreover, a direct radio connectionbetween each subscriber pair is often required.

To employ the methods known from the state of the technology, the entirenetwork topology must be known, or be ascertainable by central entities.

The topology of a network usually refers to the distribution of thesubscribers or network nodes, and their connection with one another.

It is the object of the invention to provide a method for broadcasting amessage in an incomplete radio communication network with a fluctuatingnumber of participants for forwarding the message, in which the messageis transmitted as quickly as possible and the subscribers do notnecessarily have radio contact with one another at all times.

The object is accomplished by a method for broadcasting a message in anincomplete radio communication network having a fluctuating number ofsubscribers for forwarding the message, in which each subscriber has atransmitting and receiving device for messages and a positioning systemfor determining his global position. In accordance with the invention,after receiving the message, subscribers determine their own positionand the distance d from the sender of the message, who is likewise asubscriber, and forward the message, with their position, to furthersubscribers after a predetermined waiting period t, which decreasesmonotonically as the distance 2 increases.

The method assures an optimum broadcasting of messages, particularly ofshort messages, data packets and status reports, in a radiocommunication network when the subscribers have no information about thenetwork topology. The message is transmitted rapidly, from a subscriberacting as the sender of the message to be transmitted, to at least onefurther subscriber of the partial network; not all subscribers must bewithin range of the sender of the message.

Unlike approaches known from the state of the technology, the methodtakes into account the limited knowledge of individual subscribers inthe mobile, decentralized radio communication network. The subscribersneed not be aware of the complete topology of the network. The methodoptimizes the message broadcasting with the presupposition of littleknowledge about network subscribers and the actual network.

The presupposition that it is not necessary for each subscriber to befamiliar with the network topology is practical and reasonable, becausethe topology can change continuously due to the considerable mobility ofsome of the subscribers.

A typical example from traffic technology serves to explain this: Atwo-vehicle accident has occurred on a road. The message about theaccident is transmitted to the surroundings by at least one of theinvolved motor vehicles, as the initiator. The target region for themessage includes, for example, a target space having a semicircularoutline and a radius of about 10 kilometers. All motor vehicles locatedwithin this target space make up the target group for the message aboutthe accident. The position and number of the receivers normally changeover time. Therefore, precise knowledge of the network topology insidethe target space at a certain time does not assure a necessary quantityof information.

The message transmitted by the first subscriber preferably includes ageometrical description of the target region for his message.

The determination of the boundary of the target region can clarify inadvance to which group of receivers the message should be transmitted sothat it is put to good use.

In particular, the subscribers can use a decision function to determinetheir association with the target region, and only forward the messageif they are associated with it. In addition to the geometrical boundaryof the target region, other decision criteria can be relevant for thedecision of whether or not the subscribers are associated with theprovided target region.

In a further embodiment of the invention, the subscribers only forwardthe received message to further subscribers after the first reception ofthe message. After receiving the message, each subscriber determineswhether he is receiving the message for the first time. For thispurpose, the subscriber checks a list that includes a message keyrelating to a unique association of previously-received messages withthe respective sender. If the subscriber has already received themessage, he engages in no further activities, because he has alreadyforwarded the message to further subscribers. This avoids unnecessaryoccupation of the radio communication network.

The waiting period t between reception and transmission preferablydecreases exponentially as the distance d between the communicatingsubscribers increases. This structuring of the predetermined waitingperiod t has proven particularly advantageous in trials.

The dependent claims disclose further advantageous embodiments.

The invention is described in detail below by way of exemplaryembodiments illustrated in the drawing figures. Shown are in:

FIGS. 1-3 scenarios for broadcasting messages, in a schematicrepresentation; and

FIG. 4 the waiting period t as a function of the distance d between twosubscribers.

FIGS. 1 through 3 schematically illustrate an incomplete radiocommunication network 2. A network is defined as incomplete if no directradio connection exists between each subscriber of the network. Theradio communication network 2 usually has a fluctuating number ofsubscribers 4 through 12. Dashed-line paths 14 and arrows 16 describepossible direct radio connections between two respective subscribers 4through 12.

Each subscriber 4 through 12 has a transmitting and receiving device formessages, and a positioning system for determining his global position.

FIG. 1 describes the scenario of the radio communication network 2 at atime t₁. A subscriber 4 transmits a message into the surrounding space,thereby also transmitting his global position. An omnidirectionalaerial, for example, can assist in radiating the message.

Subscribers 6 receive the message sent by the subscriber 4, with theinformation about his global position. Arrows 16 indicate the possibleradio connections with the subscriber 4 at the time t₁. The message sentby the subscriber 4 contains a description of the target region for hismessage. The target region need not be limited for all applications,however.

In the present situation, the first subscriber 4 can reach foursubscribers 6, 12 due to the technical marginal conditions. Only thesubscribers 6 are located in the predetermined target region 18, whichis limited by the dotted, closed line 20.

In a further exemplary embodiment, not shown, no target region isprovided. In other words, the neighboring subscriber 12 can also receivea message from the subscriber 4.

For the sake of a clear overview, circles that are not filled inrepresent the subscribers 6 shown in FIG. 1.

The constellation shown here could appear in roadway traffic, forexample. The subscriber 4 would be, for example, a motor vehicle that isstranded due to engine trouble, and is interfering with trafficapproaching from behind. The stranded subscriber 4 could transmit amessage to the subscribers 6, that is, motor vehicles approaching frombehind in the same direction, in order to inform these vehicles of theengine trouble of the subscriber 4. This could prevent traffic jams.

Ideally, an appropriate message would have to be transmittedautomatically, without driver involvement. Had the subscriber 4experienced a traffic accident, for example, the driver may not even becapable of transmitting messages.

The subscribers 6 determine their own position, for example with amethod based on the Global Positioning System (GPS), and their distancefrom the subscriber 4. At a time t₂, with t₂>t₁, the message from thesubscriber 4, with his global position, is forwarded from thesubscribers 6 to further subscribers 8 (FIG. 2) after a predeterminedwaiting period t, which decreases as the distance d between thesubscribers 4, 6 increases. In this embodiment, the subscriber 6 onlyforwards the message if he is receiving it for the first time. Thisavoids an unnecessary establishment of radio connections between thesubscribers 4 through 12.

Because t₂ is a function of the predetermined waiting period t, and thusthe distance between the subscribers, subscribers 6 in the vicinity ofthe subscriber 4 may not even have transmitted the message at the timet₂. The neighboring subscribers 6 first forward the message to furthersubscribers 8 at a time t₃, with t₃>t₂ (FIG. 3).

Another option is for the subscribers 6 through 10, as receivers of themessage from the first subscriber 4, to determine their association withthe target region 20 with the aid of a decision function. A geometricalassociation with the target region 20 may not suffice in and of itself,so at least one further decision function is used in assessing theassociation with the target region.

The diagram in FIG. 4 depicts the exponential decrease in the waitingperiod t as a function of the distance d between two subscribers 4through 10, particularly between the first subscriber 4 and secondsubscribers 6. This ensures that subscribers 6 through 10 are preferablyprovided at the edge of the target region for rapid forwarding of themessage of the first subscriber 4; this ensures, among other things, arapid, effective broadcasting of the message of the first subscriber 4.Depending on the scenario, however, other functional dependencies of thewaiting period t on the distance d can also be used. In particular,different functional dependencies within the partial network can also beused.

The message is forwarded from the subscribers 6 through 10 to thesubscribers 6 through 12 in the radio communication network until all ofthe subscribers 6 through 12 have received the message. In a furtherembodiment, the message is provided with a counter, which tallies thenumber of completed transmissions of the message; here, the message isforwarded until a predetermined value for the count of the counter hasbeen attained.

The method according to the invention assures an optimum broadcasting ofmessages, particularly short messages, data packets and status reports,in the radio communication network 2.

What is claimed is:
 1. A method for broadcasting a message in anincomplete radio communication network (2) having a fluctuating numberof subscribers (4-12) for forwarding the message, with each subscriberhaving a transmitting and receiving device for messages, and apositioning system for determining his global position, characterized inthat subscribers (6-12) determine their own position and the distance dfrom the sender of the message after receiving the message, and forwardthe message, with their position, to further subscribers (6-12) after apredetermined waiting period t, which decreases monotonically as thedistance d increases.
 2. The method according to claim 1, characterizedin that subscribers (6-12) only forward the received message afterreceiving it for the first time.
 3. The method according to claim 1,characterized in that the transmitted message contains a geometricaldescription of a target region (20) for the message.
 4. The methodaccording to claim 3, characterized in that subscribers (6-12) can use alocal decision function to determine their association with the targetregion (20), and only forward the message if they are associated withthe target region (20).
 5. The method according to claim 1,characterized in that the message is provided with a counter, whichtallies the number of completed transmissions of the message, with themessage being forwarded until a predetermined value for the counter hasbeen attained.
 6. The method according to claim 1, characterized in thatthe waiting period t decreases exponentially as the distance d betweenthe communicating subscribers (6-12) increases.
 7. The method accordingto claim 1, characterized in that the message contains the globalposition of an event.
 8. The method according to claim 1, characterizedin that the global position is determined in accordance with a methodbased on the Global Positioning System (GPS).
 9. The method according toclaim 1, characterized in that an omnidirectional aerial transmits themessage.